Molecular dynamics simulations of shock-induced deformation twinning of a body-centered-cubic metal

Abstract

Despite a number of previous nonequilibrium molecular dynamics (MD) studies into plasticity in face-centeredcubic metals, and phase transitions in body-centered-cubic (bcc) metals, the plastic response to rapid compression of bcc metals remains largely unexplored. Key questions remain as to the relative importance of dislocation motion and twinning in shear stress release and consequent strength. We present here large scale MD simulations of shock compressed bcc metal, using an extended Finnis-Sinclair potential for tantalum, and demonstrate the presence of significant deformation twinning for pressures above the Hugoniot elastic limit for shock waves propagating along the [001] direction. The twinned variants are separately identified by a per atom order parameter, allowing the strain and stress states of the rotated material to be studied. The atomic motion during twinning, and thus its mechanism, for this potential, is identified by use of a three-dimensional pair-correlation function.

X-ray diffraction measurements of plasticity in shock-compressed vanadium in the region of 10–70 GPa

“…122, 025117 (2017) and as seen in the continuum modelling of deformation twinning by, for example, Kochmann and Le. 44 It finds a clear parallel in the MD simulations of tantalum single crystals shocked along the [001] direction by Higginbotham et al 12 and Tramontina et al, 13 and we noted in Sec. III that in our experiment, the plane of maximum resolved shear stress in the vanadium-foil sample is close to the (112) twin composition planes for grain orientations with a high probability of occurrence.…”

“…8,[12][13][14] There are little available experimental data on the highstrain-rate yield strength of vanadium. The limited number of publications that are available appears to show some inconsistencies, although they arise from experiments carried out under conditions of very different strain rates and length-and timescales and used material samples of possibly different initial microstructures.…”

“…Higginbotham, Suggit et al, 12 and Tramontina et al 13 have provided non-equilibrium molecular-dynamics (MD) simulations for single-crystal tantalum shock compressed along the [001] direction. The work by Tramontina et al specifically include some pre-existing defects, which act as dislocation sources, and note the progressive importance of deformation twinning as a mechanism of plastic response, as the shock pressure increases: dislocations dominate at the lowest pressures, a combination of dislocations and twins is evident at $30 GPa, and twins dominate above 70 GPa.…”

Simulations of in situ x-ray diffraction from uniaxially compressed highly textured polycrystalline targets

“…The shuffling then has the effect of causing the crystal to be reflected in the (112) twinning plane. Note that as crystal is uniaxially compressed, this causes the [001] direction to be reflected to the [111] direction of the compressed crystal, rather than the [221] direction expected under hydrostatic conditions (see Figure 6 of Higginbotham et al 66 ). Lastly, the twinned material returns towards the hydrostat, by relaxing along the longitudinal direction and compression along the transverse directions in the new rotated coordinates.…”

Femtosecond X-Ray Diffraction Studies of the Reversal of the Microstructural Effects of Plastic Deformation during Shock Release of Tantalum

“…Shock-induced plasticity in tantalum, a body-centered cubic metal, has been studied extensively, with post facto analyses [6,[16][17][18][19] being complemented by a number of MD studies [9,[20][21][22][23]. Here we use XRD to directly monitor lattice orientations during shock release.…”